A microphone has at least one transducer assembly, known as a “capsule”, which detects sound waves and converts the detected sound waves into an electrical signal. A condenser microphone has a capsule typically comprising a metal disc, known as a “backplate”, fixed in a spaced apart position and insulated from a metal (or metal plated) diaphragm. The backplate and diaphragm are connected to electrical connectors and act as opposing plates of a capacitor, having a capacitance directly proportional to the size and spacing of the diaphragm and backplate. The components and spacing dimensions in the condenser microphone capsule are typically very small, with the diaphragm being approximately 6 um thick and spaced apart from the backplate by approximately 40 um.
When the diaphragm is vibrated due to sound waves, it moves towards and away from the backplate, varying the spacing between the diaphragm and the backplate and causing a change in capacitance. When an appropriate electrical circuit is connected to the backplate and diaphragm, the change in capacitance is detected and an electrical signal is generated.
The condenser microphone backplate includes an assembly comprising a planar metal disc and a mount, the mount adapted to connect the disc to a capsule assembly and insulate the disc from the diaphragm. For a considerable length of time, backplate assemblies have been produced by initially fabricating the metal disc using a milling process; over-moulding a plastic mount around the perimeter of the disc; a second stage of milling to finish the planar surfaces and fabricate an array of first apertures in the disc and mount in a first direction, perpendicular to the planar surfaces of the disc; a third stage of milling to fabricate one or more second apertures in the disc and mount in a second direction, parallel to the planar surfaces; and tapping the second apertures to allow electrical connectors to threadably engage with the disc. The backplate assembly is then connected to the capsule assembly by a plurality of fasteners connected through some of the first apertures.
Whilst this process of producing backplate assemblies has been practiced successfully for some time, it has a number of drawbacks. For example, the process has many different stages, each stage adding complexity, margin for error and cost. This is particularly the case when further machinery is required to perform each additional step of the process. Also, the stage of milling and tapping the second apertures can prove problematic as this can distort the plastic mount, which consequently can affect the spacing between the backplate and the diaphragm and degrade the quality of electrical signal generated by the capsule.
Accordingly, it would be useful to provide an alternative backplate assembly for a condenser microphone capsule which is produced by a simpler, quicker, more consistent and/or more cost effective process than the prior art approaches.